This invention relates to a pump drive circuit, and more particularly to a pump drive circuit which can control the driving of a pump by controlling the phase of a voltage supplied to the pump.
There is known a conventional pump drive circuit for driving a pump through control of voltage phase angle. However, this type of pump drive circuit has the problem that, when the power source has a frequency of 50 Hz or 60 Hz, controlling the voltage supply at even the same phase fails to produce the same flow rate of air or water. The closer the pump comes to a state of being driven at full power, the greater the difference between the pump outputs resulting from the difference in frequency, and thus, the more significant the problem. With respect especially to a pump drive circuit involved in the air or water supply (or as a suction device) of an endoscope, a fine adjustment of flow rate is demanded, which makes it necessary to remove any difference in pump outputs attributable to a difference in frequency.